As the critical dimension of device features decreases, the thickness of an amorphous carbon mask layer must be increased in order to allow the mask layer to endure while etching underlying layers. However, the increased thickness of the amorphous carbon layer negatively impacts wafer translucence. In order to overcome increasingly thick amorphous carbon mask layers, a boron doped amorphous carbon mask layer is used.
A boron-doped amorphous carbon layer is not photosensitive and is instead patterned with a plasma etch to accurately reproduce a pattern of an overlying photosensitive layer. The greater plasma etch resistance of boron-doped carbon layers is such that a fluorocarbon species such as CxFy or CxHyFz species and high RF bias power, is required to etch the boron-doped amorphous carbon layer. However, the inventors have observed that this etch process results in the formation of residual polymers (i.e. fluorocarbon residues) proximate the bottom of the features patterned into the boron doped carbon layers, thereby making it difficult to obtain a vertical profile in the feature.
Thus, the inventors have provided improved methods for removing residual polymers formed during etching of a boron-doped amorphous carbon layer.